1. Field of the Invention
The present invention relates to a process planning method which makes it possible to design an optimum process including the size of cutting tools to be used and machining order in machining a workpieces into the desired shape with a machine tool equipped with end mills serving as cutting tools. The invention also relates to a process planning apparatus constituted to perform the method mentioned above. Furthermore, the invention relates to a recording medium in which computer programs are stored for executing the above-mentioned method with a computer.
2. Description of Related Art
An NC (Numerical Control) machine for moving a cutting tool along a tool path defined in advance numerically relative to a workpiece fixed on a machine table and thereby machining the workpiece in a predetermined manner is extensively adopted for the cutting processes for machining workpieces into various configurations with end mills used as cutting tools, besides drilling processes as for which the drills, are used as cutting tools, and tapping processes for which the taps are used as cutting tools.
When machining with the NC machine of the above-mentioned kind is implemented, a process planning is performed first to determine cutting tools to be used, machining processes with the respective cutting tools, and the contents of work in each machining process, according to a final machining shape. Next, an NC program is prepared to set tool paths according to the results of the process planning, together with a feed rate in each part on the respective tool paths, and then machining is performed by operating the cutting tools and machine table based on the servo control according to the NC program.
The applicant of the present invention has already proposed an NC program generating method applicable to the NC machine for which an end mills are used as a cutting tools (Japanese Patent Application Laid-Open No. 2003-263208 (2003)). This method includes the steps of: replacing a final machining shape with a plurality of fixed cycles prepared in each machining process defined as the results of a process planning; estimating cutting force exerted on the end mill on a tool path assumed in the respective fixed cycles; and determining a tool path in which the estimated value converges into an proper value together with the feed rate in each portion of the tool path. According to the method, it is possible to prepare the NC program in which both high machining efficiency and high machining accuracy can be attained while reducing the damage and excessive wear of the end mill, without relying on the operator's experience, and without the complicated work being required.
On the other hand, there have been the following problems. A process planning necessary in the pre-stage for preparing an NC program as above has so far been practiced by the designer versed in industrial technology based on his experience (past achievements), so the results of the actually prepared process planning depend on the faculty of the designer. Moreover, the results of the process planning prepared by the planner having abundant experiences are not necessarily optimum. Therefore, there is no assurance that the NC program prepared by the afore-described method based on the results of such process planning and the machining to be practiced according to such NC program are optimum from the ultimate viewpoint of reducing the composite machining cost after taking into account the machining time, the durability of the end mill, and the like. Thus, there has been the possibility of losing an opportunity of further reduction of the machining cost.
In recent years, attempts have been made to automate the process planning by dividing the complicated machining shape into plural sorts of machining features of simple shape, but those attempts are no more than to determine the order of eliminating the machining features based on the past achievements. Accordingly, they are only used as auxiliary tools for planner having little experience.